The present invention relates to transistor amplifiers in general, and in particular to a common-emitter cascode f.sub.T doubler transistor amplifier employing a feed forward non-linearity and thermal-distortion correction path.
Common-emitter cascode transistor amplifiers are very popular for use in oscilloscopes and other precision measurement instruments requiring high-band-width operation. One such common-emitter transistor amplifier exhibiting an f.sub.T characteristic that is substantially doubled is described in U.S. Pat. No. 3,633,120, which is assigned to the assignee of the present invention. The so-called f.sub.T doubler amplifier includes first and second pairs of transistors wherein the outputs of the transistor pairs are coupled in parallel while a common input current its provided in series to the four transistors to substantially double the current gain at the upper -3dB point. However, this amplifier exhibits certain non-linearities and thermal distortions which are inherent in the fundamental physical properties of the semiconductor pn junctions that are employed.
A feed-forward non-linearity and thermal distortion technique for common-emitter transistor amplifiers has been developed and is taught in U.S. Pat. No. 4,146,844, which is also assigned to the assignee of the present invention. While the feed forward technique has been applied two-transistor differential amplifiers, it would be desirable to apply this technique to the four-transistor f.sub.T doubler amplifier configuration as well.